Lawn mowers powered by an electric motor are known. An electric motor generates less noise and emits no exhaust gas, as opposed to an internal combustion. In particular, electric lawn mowers carrying a battery for driving a cutting blade via an electric motor are gaining popularity. See JPH09-201126A, for instance. Because of the absence of a power cable, the lawn mower powered by a battery can freely travel over a wide area in a comfortable manner.
However, because an electric lawn mower powered by a battery can be operated only for a time duration permitted by the limited capacity of the battery, the amount of work that can be performed, and the time duration of work are limited. Therefore, in designing a lawn mower carrying a battery, it is important to efficiently utilize the energy available from the given battery.